In a conventional printer, copier or other such image forming machine, sheets of paper or other sheet media are pulled from a stack and fed downstream into the print engine components where the desired image is formed on each sheet. This "pick/feed" operation is typically accomplished using a motor driven feed roller that has a frictionally adherent surface. The surface of the roller rotates against the upper surface of the top sheet in the stack to direct the top sheet into the print engine. As each sheet is picked and fed into the print engine, the desired image is being formed on a rotating photoconductive drum, typically using a scanning laser, according to print data transmitted to the printer from, for example, an attached computer. The image is thereafter transferred onto the sheet of paper as the paper passes along in contact with or very close proximity to the photoconducting drum.
To accurately transfer the image from the photoconducting drum to the paper, each sheet of paper should move through the image area immediately adjacent to the drum at a speed that corresponds to the rate of rotation of the drum. Also, the leading edge of the paper must reach the image area at the proper time so that the image is transferred accurately to the paper. In a typical laser printer, the scanning laser is positioned so that the photoconducting drum rotates between 150.degree. to 200.degree. before engaging the paper as the image travels from the point at which it is formed on the drum by the scanning laser to the point at which it is transferred to the paper. In conventional printers, the paper is moved at a constant speed through both the pick/feed area and the image area. Consequently, the paper must be made to move through a distance that is directly proportional to the distance the image travels along the photoconducting drum to the image area. That is, the distance between the pick/feed area and the image area is limited by the diameter of the photoconducting drum and the position of the scanning laser. The distance between the drum and the feed roller is similarly limited. For example, and using a scanner positioned 180.degree. in advance of the image area, if the feed roller is made to engage the top sheet of paper in the stack at the same time the image is being scanned onto the photoconducting drum, then the distance between the pick/feed area and the image areas must be equal to one-half the circumference of the drum (i.e., the distance the image travels before being transferred to the paper).
In order to minimize the size and cost of the printer, it is desirable to move the pick/feed area as close as possible to the image area wherein the image is transferred from the photoconducting drum to the paper. This can be accomplished by decreasing the speed of the paper in the pick/feed area relative to the speed of the image on the photoconducting drum and then increasing the speed of the paper to match the speed of the image on the drum as the paper reaches the image area. The speed of the paper can be varied by varying the rate of rotation of the sheet feed roller. This method, however, adds complexity and cost to the printer by introducing variable speed motors, reduction gears and the like.